Magnetron tube



April 24, 1962 D. GLASER ET AL MAGNETRON TUBE 2 Sheets-Sheet 1 FiledFeb. 24. 1959 April 24, 1962 D.GLASER ETAL MAGNETRON TUBE Filed Feb. 24,1959 2 Sheets-Sheet 2 F i Q- 7 JNVENTOR.

DAVAD GLAEP By ARFWD SOMMYODY we. fi

A Tram/E) United States Patent 3,031,594 MAGNETRON TUBE David Glaser,Middlesex, and Arpad Somlyody, Raritan, N.J., assignors to BurroughsCorporation, Detroit, Mich., a corporation of Michigan Filed Feb. 24,1959, Ser. No. 795,068 12 Claims. (Cl. 313-157) This invention relatesto magnetron-type electron discharge tubes and to improvements in theconstruction of such tubes, particularly in the magnet used with suchtubes.

One form of magnetron tube, to which the principles of the inventionapply, includes an electrode assembly which comprises an elongatedcentral cathode and a plurality of groups of elongated electrodessurrounding the cathode and secured together at their opposite ends bymeans of insulating end disks or plates. All of the electrodes aresubstantially parallel to each other. A cylindrical magnet surrounds theelectrode assembly. In operation of this type of tube, current flowsfrom the can tral cathode to one of the groups of electrodes at a time.It has been found that some of the electrons in the beam from thecathode tend to flow toward the ends of the electrode assembly wherethey strike the insulating end disks which support the electrodes. Ithas been found that this electron bombardment of the insulating diskscauses them to become electrically charged, with the result that theelectric field in the tube becomes distorted and electron flow isadversely afiected.

The objects of the present invention are concerned with an improvedconstruction for a magnetron tube in which electron flow is controlledso that spurious effects on the magnetic and electric fields in the tubeare minimized and tube operation is improved.

In brief, a magnetron-type electron tube embodying the inventionincludes, in a suitable envelope, an electrode assembly including acentral longitudinally elongated cathode surrounded by groups oflongitudinally elongated electrodes which are adapted to form andreceive an electron beam from the cathode. The various electrodes aresecured together parallel to each other by means of insulating end diskssecured to the opposite ends of the electrodes. A cylindrical permanentmagnet surrounds the tube envelope and the electrodes contained therein.The axis of the magnet is coaxial with the longitudinal axis of theenvelope and the electrode assembly. 'The magnet provides a longitudinalmagnetic field in the envelope which combines with the electric fieldtherein to control the flow of electrons from the cathode to the groupsof electrodes.

According to the invention, the magnet is adapted to control the flow ofthe electrons so that they strike the electrodes substantially at theircenters and are substantially prevented from fanning out and strikingthe insulating end plates of the electrode assembly. Thus, the endplates do not become electrically charged and they do not adverselyafiect electron flow. The desired result may be achieved in severalways. According to one aspect of the invention, the permanent magnet ismodified by the provision of an auxiliary region of material which hashigh magnetic permeability but is not permanently magnetized. Thus, thisregion does not produce magnetic lines of force. The auxiliary region ofnon-magnetized material may be in the form of a ring and is positionedso that it surrounds substantially the center of the electrodes in theelectrode assembly. The auxiliary ring modifies the magnetic fieldproduced by the permanent magnet so that electrons tend to flow towardthe centers of the electrodes and not to the ends thereof. In anotherarrangement, the magnet is physically shaped to provide the desiredmagnetic field con- Patented Apr. 24, 1962 figuration to prevent theelectrons from flowing out toward the ends of the electrodes.

The invention is described in greater detail by reference to thedrawing, wherein:

FIG. 1 is a perspective view of a magnetron beam switching tubeembodying the invention;

FIG. 2 is a sectional view of the magnet shown in FIG. 1 and two of themagnetic flux lines generated thereby;

FIG. 3 is a sectional view of a magnet of the type used in the prior artandsome of the flux lines generated thereby;

FIG. 4 is an elevational view, partly in section, of the tube of FIG. 1and a modified magnet embodying the invention;

FIG. 5 is an elevational view, partly in section, of the tube of FIG. 1and another modification of the magnet of the invention;

FIG. 6 is an elevational view, partly in section, of the tube of FIG. 1and another modification of the magnet of the invention; and

FIG. 7 is an elevational View, partly' in section, of the tube of FIG. 1and another modification of the magnet of the invention.

The principles of the invention are applicable to magnetron tubes and,particularly, to a magnetron beam switching tube, type 6700. This typeof tube is shown in FIG. 1 as tube 10 and includes, briefly, an envelope12 which contains an electrode assembly 13 including a centrallongitudinally elongated cathode 14 and ten groups of electrodes spacedradially equidistantly from the cathode and surrounding the cathode andparallel to each other and to the cathode. Each group of electrodesincludes a generally U-shaped elongated spade electrode 16 and agenerally L-shaped target electrode 18 positioned so that each targetoccupies the space between adjacent spade electrodes. Each spadeelectrode serves to form and hold an electron beam on its associatedtarget electrode. A generally rod-like switching electrode 20 is alsoincluded in each group of electrodes and is positioned between one edgeof each target electrode and the adjacent spade electrode. The Switchingelectrodes are known as switching grids. The electrodes of the cage 13are secured together by means of top and bottom insulating end disks 22and 24, respectively, of mica or the like, which have inner facingsurfaces 26 and 28 that are accessible to electrons flowing from thecathode to the other electrodes. The mica disks are provided withsuitable apertures 30 to receive and secure end portions of theelectrodes, as is Well known in the art.

An open-ended cylindrical permanent magnet 32 is provided surroundingthe tube envelope and coaxial therewith. The magnet is secured to thetube envelope, for example, by means of a layer 34 of a suitable plasticmaterial. The magnet provides an axial magnetic field which is utilizedin conjunction with electric fields within the tube to form and switchan electron beam from the cathode to each of the groups of electrodes.The direction in which the beam switches, that is clockwise orcounter-clockwise, is always the same and is determined by theorientation of the electric and magnetic fields.

Briefly, in operation of the tube 10, electrons emitted by the cathodeare retained at the cathode if each of the spades, targets and switchinggrids carries its normal operating electrical potential. When a spade orswitching grid experiences a suitable lowering of its potential, anelectron beam is formed and directed to the corresponding targetelectrode. Ordianrily with a cylindrical magnet, the electrons in thebeam tend to flow out toward the ends of the electrode assembly 13 and,in addition, some electrons strike the mica disks 28 and 30. Suchelectron bombardment of the mica disks would ordinarily cause the disksto become electrically charged and then adversely affect electron flowin the tube.

According to the invention, the magnet 32 is constructed to provide amagnetic field within the tube of such configuration that the electronsin a beam are substantially' prevented from flowing toward the ends ofthe electrode assemby and are substantially limited to the centralregion of the tube electrodes between the end disks 2 8 and 30. Thus,electrons are substantially prevented from striking and charigng the endplates or other surfaces in the tube.

In one embodiment of the invention, referring to FIG. 1, the desiredresults are achieved with a magnet 32 having two end rings 36 and 38 ofhigh reluctance, permanently magnetized material, which generatemagnetic lines of force, and an intermediate ring 40 of comparativelyhigh permeability material which, preferably, cannot be permanentlymagnetized and does not generate magnetic lines of force. The end rings36 and 38 may be made of Alnico VI, for example, and the ring 40 may bemade of soft iron. The ring 40 is positioned in the magnet so that itsurrounds the region of the tube 10 in which it is desired to maintainthe electron beam. Thus, in the present embodiment, the ring 40 ispositioned so that it surrounds thte electrode assembly at about itslongitudinal center.

The general shape of magnetic field provided by the magnet 32 isillustrated in FIG. 2 by flux lines 41, and the magnetic field generatedby a similar cylindrical permanent magnet 42 of uniform construction andnot having the ring 40 is illustrated by lines 43 in FIG. 3. Themagnetic lines of flux generated by the magnet t2 shown in FIG. 3 aresmoothly curved and bow outwardly from the body of the magnet toward theaXis of the magnet. Flux lines of this shape tend to cause someelectrons to flow outwardly toward the ends of tthe elecrode assembly.In the magnet 32 of FIG. 2, the magnetic flux lines leave the ends ofthe magnet as they do in the magnet 44, but in the region of the ring 40they bend outwardly toward the main body of the magnet. With this shapeof magnetic field, all electrons tend to flow toward the ring 40. Thus,if the ring 40 is properly positioned with re spect to the tubeelectrodes, substantially all electrons can be directed to the desiredregion of the tube electrodes.

in a type 6700 tube, the electrodes have a length of about 1 inch, andthe magnet has a total length of about 1% inches. The ring 40 has alength of about Mr inch. The magnet is also magnetized so that the endrings have a magnetic flux density of about 450 gausses. The rings 36and 38 have a reluctance of about 10, and the ring 40 has a reluctanceof about .01.

In a modification of the invention shown in FIG. 4, the tube '10 mayemploy a permanent magnet 44 of onepiece construction, for example, ofthe same material as the end pieces 36 and 38 of the magnet 32. A ringor band 45 of the same material as the ring 40 is provided surroundingthe magnet 44 and slidably mounted thereon. The ring 45 is properlypositioned on the magnet to orient the electron beam as desired.

If desired, a one-piece permanent magnet, suitably shaped, may be usedto practice the invention. One such magnet as shown in FIG. is in theform of a cylinder having a concave inner Wall Thus, the magnet 4-6 hasa thin central region and thick end portions 50, a construction whichprovides the desired magnetic field configuration. Alternatively, asshown in FIG. 6, the magnet 46 may have a flat, rather than concave,inner wall 52 as seen in cross-section. In addition, the desired resultmay be achieved in a magnet 54 (FIG. 7) having a concave outer wall 56.

The effect of the magnet construction of the invention was studied intype 6700 tubes in which the target elec trodes were divided into threeseparate portions, top, bottom, and central portions. Tubes havingconventional magnets were compared with tubes having magnets of theinvention, and it was found that in the conven-' tional tube thecurrents from the top, bottom, and cen-' tral portions of the targetswere substantially the same with a typical value for each section beingabout milliamperes. Tubes using magnets embodying the inabout 3 .5milliamperes.

in the tube substantially to the central portions of the targetelectrodes. With this orientation of the current, the mica end plates donot become charged and do not adversely affect the operation of thetube. Thus, tube operation is more uniform than heretofore.

What is claimed is:

1. A magnetron beam switching tube adapted to operate with crossedelectric and magnetic fields including a cathode and a plurality ofgroups of electrodes; each group including a target electrode whichreceives an elec-- tron beam and produces an output signal therefrom, aspade electrode which holds an electron beam on its as' sociated targetelectrode, and a switching electrode which;

serves to switch an electron beam from one group of electrodes to thenext; and a hollow cylindrical magnet surrounding said cathode and saidgroups of electrodes; said magnet having regions of different magneticcharac-' teristics whereby a magnetic field configuration is provided insaid tube which substantially prevents electrons from flowing to theends of said electrodes and directs them toward the centers of saidelectrodes.

2. A magnetron beam switching tube adapted to op rate with crossedelectric and magnetic fields including a cathode and a plurality ofgroups of electrodes; each group including a target electrode whichreceives an electron beam and produces an output signal therefrom, aspade electrode which holds an electron beam on its associated targetelectrode, and a switching electrode which serves to switch an electronbeam from one group of electrodes to the next; and a hollow cylindricalmagnet surrounding said cathode and said groups of electrodes; saidmagnet including means for directing the flow of electrons from saidcathode toward the longitudinal center of the electrodes of the tube andpreventing the flow of electrons toward the ends of said electrodes.

3. A magnetron beam switching tube adapted to operate with crossedelectric and magnetic fields including a cathode and a plurality ofgroups of electrodes; each group including a target electrode whichreceives an electron beam and produces an output signal therefrom, aspade electrode which holds an electron beam on its associated targetelectrode, and a switching electrode which servesto switch an electronbeam from one group of electrodes to the next; and a hollow cylindricalmagnet surrounding said cathode and said groups of elec-.- trodes; saidmagnet having a body of magnetic but unmagnetized material associatedtherewith to control the configuration of the magnetic field in saidtube to direct electrons generally away from the ends of satidelectrodes and toward their centers.

4. The tube defined in claim 3 wherein said magnet includes integraltherewith a ring of material having high magnetic permeability butunmagnetized.

5. The tube defined in claim 3 wherein said magnet includes a ring ofmaterial having high magnetic permeability but unmagnetizedsubstantially at the center thereof.

6. The tube defined in claim 3 wherein said magnet includes a ring ofmaterial having high magnetic permeability but unmagnetized, said ringbeing positioned between two rings of permanent magnet material.

7. The tube defined in claim 3 wherein said magnet consists of outerportions of permanent magnet material and an intermediate ring'ofhigh-permeability unmagnetized material. 7

8. A magnetron beam switching tube adapted to operate with crossedelectric and magnetic fields including a cathode and a plurality ofgroups of electrodes; each group including a target electrode whichreceives an electron beam and produces an output signal therefrom, aspade electrode which holds an electron beam on its associated targetelectrode, and a switching electrode which serves to switch an electronbeam from one group of electrodes to the next; and a hollow cylindricalmagnet surrounding said cathode and said groups of electrodes; saidmagnet having a thin central region and thick end portions.

9. A magnetron beam switching tube adapted to operate With crossedelectric and magnetic fields including a cathode and a plurality ofgroups of electrodes; each group including a target electrode whichreceives an electron beam and produces an output signal therefrom, aspade electrode Which holds an electron beam on its associated targetelectrode, and a switching electrode which serves to switch an electronbeam from one group of electrodes to the next; and a hollow cylindricalmagnet surrounding said cathode and said groups of electrodes; saidmagnet having a concave inner wall.

10. A magnetron beam switching tube adapted to operate with crossedelectric and magnetic fields including a cathode and a plurality ofgroups of electrodes; each group including a target electrode whichreceives an electron beam and produces an output signal therefrom, aspade electrode which holds an electron beam on its associated targetelectrode, and a switching electrode which serves to switch an electronbeam from one group of electrodes to the next; and a hollow cylindricalmagnet surrounding said cathode and said groups of electrodes; saidmagnet having a concave outer wall.

11. The tube defined in claim 3 and including in operative relationshipwith said magnet a ring of material having high magnetic permeability.

12. A magnetron beam switching tube including an envelope, an electrodeassembly in said envelope, said electrode assembly having a longitudinalorientation in said envelope and including a central cathode and aplurality of electron-receiving electrodes surrounding said cathode,permanent magnet means providing a longitudinal magnetic field in saidenvelope, said magnetic field operating with the electric field in saidtube to control the flow of electrons from said cathode to saidelectronreceiving electrodes, and auxiliary magnetic means in operativerelation with said permanent magnet means altering the shape of thelongitudinal magnetic field produced thereby whereby the flow ofelectrons from said cathode is limited to a selected region of saidelectron-receiving electrodes.

References Cited in the file of this patent UNITED STATES PATENTS1,387,985 Hull Aug. 16, 1921 1,617,172 Smith Feb. 8, 1927 2,246,121Blewett June 17, 1941 2,390,884 Jansky Dec. 11, 1945 2,418,469 HagstrumApr. 8, 1947 2,839,702 Fan June 17, 1958

